DESCRIPTION: Previous studies from this lab provided evidence that postnatal brain development in olfactory and somatosensory cortices is mainly constructive, and that neural activity foments postnatal elaboration of circuitry. The present proposal addresses the question of why the brain adds enormous numbers of neuronal branches and synapses postnatally in an activity-dependent manner, especially since this entails jeopardy from the effects of deprivation. A review of the evidence in anthropoid primates suggests that the expression of ocular dominance columns in visual cortex is related to animal size. The first aim of the study is to confirm the validity of this 'size' principle among several carnivores and prosimians. The second aim is to determine whether the size principle results from differences in the duration of asynchronous binocular activity during development. This will be tested by 1) attempting to generate ocular dominance columns in animals which normally do not express them; and 2) directly following the formation and modulation of ocular dominance columns with optical imaging during development. A third aim will be to explore in humans the hypothesis the activity-dependent construction of the visual world serves to establish neural associations that allow a correct interpretation of an inherently ambiguous visual world (the consensus at the present is that activity acts primarily to validate and refine receptive field properties). This will entail an analysis of 1) the perception of transparent 3-D objects; and 2) the relationship between biases in the perception of oriented contours and the prevalence of differently oriented contours in the visual world. The results of these several projects should indicate whether the prolonged postnatal period of activity-dependent plasticity in mammals plays a largely permissive role, or whether it enables experience to make the visual associations that allow us to see normally.